The present invention relates to systems for distributing and playing digitized audiovisual signals and, in particular, to a mechanism for distributing and playing such digitized audiovisual signals such that unauthorized copying of such signals is discouraged to thereby protect intellectual property rights of artists.
Recent advances in lossless compression of digitized audio signals and storage capacity has recently led to the development of music players which play CD-quality music stored in solidstate memory. For example, a number of MP3 players are available into which a user can download compressed, CD-quality digitized audio signals into solid-state memory for subsequent playback. xe2x80x9cMP3xe2x80x9d generally refers to the MP3 format which is the MPEG standard for audio coding (MPEG-1 Video, Layer 3 Audio, ISO Standard #1172-3). The MP3 format provides excellent sound quality at a data rate of 128 Kbits (44 KHz, 16-bit samples, stereo).
While MP3 players provide very good sound quality and great convenience for the user, MP3 players provide essentially no protection whatsoever against unauthorized copying of copyrighted works. Currently, a number of computer systems provide free access to copyrighted musical works through the Internet. A user who is in possession of a digitized, copyrighted music signal in the MP3 format can, albeit most likely in violation of copyright laws, distribute unlimited identical digital copies of the music signal to friends with no compensation whatsoever to the copyright holder. Each such copy suffers no loss of quality from the original digitized music signal.
A few attempts have been made to thwart the unauthorized proliferation of perfect digital copies of digitized audiovisual signals. One such technique is used in minidisc and digital audio tape (DAT) devices. To allow transfer of previously purchased digitized audio signals, one digital-to-digital copy is permitted. In other words, digital copies of digital copies is prevented. Typically, a single bit in the storage medium indicates whether the stored signal is a digital copy. If content is written to the storage mediumxe2x80x94e.g., either a minidisc or a DAT tapexe2x80x94through a digital port in a player/recorder, the bit is set to indicate that the content of the medium is a digital copy. Otherwise, the bit is cleared to indicate either an analog copyxe2x80x94content recorded through an analog port of the player/recorderxe2x80x94or that the content is an original recording, e.g., through a microphone.
This form of copy protection is insufficiently restrictive. For example, an owner of an audio DAT can distribute at least one unauthorized copy to another person. In addition, unlimited digital copies of a CD can be made onto minidiscs or DATs although each of those digital copies cannot be digitally copied. This form of copy protection can also be excessively restrictive, preventing an owner of a prerecorded audio medium to make copies for each of a number of players of the prerecorded audio owner, namely, players in the home, office, car, and for portable use.
As alluded to briefly above, the single-copy mechanism fails to prevent any copying of digital read-only media such as CDs. The content of such media is typically uncompressed and un-obscured such that unauthorized copying is unimpeded.
What is needed is a mechanism by which copyrightable content of digital storage media is protected against unauthorized copying while affording the owner of such digital storage reasonable unimpeded convenience of use and enjoyment of the content.
In accordance with the present invention, data such as a musical track is stored as a secure portable track (SPT) which can be bound to one or more specific external players and can be bound to the particular storage medium in which the SPT is stored. Such restricts playback of the SPT to the specific external players and ensures that playback is only from the original storage medium. Such inhibits unauthorized copying of the SPT.
The SPT is bound to an external player by encrypting data representing the substantive content of the SPT using a storage key which is unique to the external player, is difficult to change (i.e., is read-only), and is held in strict secrecy by the external player. Specifically, the data is encrypted using a master media key and the master media key is encrypted using the storage key. Since only the external player knows the storage key, the master media key is passed to the external player using a secure communication session and the external player encrypts the master media key using the storage key and returns the encrypted master media key. Accordingly, only the specific external player can decrypt the master media key and, therefore, the data representing the substantive content of the SPT.
The SPT is bound to a particular piece of storage medium by including data uniquely identifying the storage medium in a tamper-resistant form, e.g., cryptographically signed. The medium identification data is difficult to change, i.e., read-only. Prior to playback of the SPT, the external player confirms that the media identification data has not been tampered with and properly identifies the storage medium.
The SPT can also be bound to the storage medium by embedding logic circuitry, e.g., integrated circuitry, in the packaging of the storage medium for performing cryptographic processing. The SPT is bound by encrypting the master media key, which is used to encrypt the data representing the substantive content of the SPT, using the embedded logic. By using unique cryptographic logic in the packaging of the storage medium, only that particular storage medium can decrypt the master media key and, therefore, the substantive content of the SPT.
To allow a user to playback the SPT on a number of players, e.g., one in the home, one in the office, one in the car, etc., external players can share storage keys with one another. However, such key sharing must be done in a cryptographically secure manner to prevent crackers from attempting to collect storage keys from external players.
The two external players communicate with one another in a cryptographically secure session. One, the initiator, sends a request message which includes a certificate of the initiator and a first random number. The other, i.e., the responder, authenticates the initiator using the certificate and responds with a reply message. The reply message includes the certificate of the responder, the first random number, a second random number, and one or more storage keys of the responder encrypted with a public key of the initiator. The initiator authenticates the responder using the certificate and responds with an exchange message. The exchange message includes the first and second random numbers and one or more storage keys of the initiator encrypted with a public key of the responder. Thus, each has copies of the other""s storage keys and can play SPTs bound to the other external player.
Before downloading an SPT to a particular external player, the ability of the external player to enforce restrictions placed upon the SPT is verified. During a registration process, the external player identifies those types of restrictions which can be enforced by the external player. Such types include a maximum number of times an SPT is played, an expiration time beyond which the SPT can no longer be played, and a number of copies of the SPT which can be made. For each type of restriction imposed upon a particular SPT, the external player is verified to be able to enforce that particular type of restriction,. If the external player is unable to enforce any of the restrictions imposed upon the SPT, downloading and/or binding of the SPT to the external player is refused. Otherwise, downloading and/or binding is permitted.